1. Field of the Invention
The present invention relates generally to image forming apparatuses, methods of controlling carriage travel in image forming apparatuses, and non-transitory computer-readable storage media storing a program for causing a computer to execute such methods, and more particularly to an image forming apparatus including a recording head configured to eject liquid droplets, a method of controlling carriage travel in the image forming apparatus, and a non-transitory computer-readable storage medium storing a program for causing a computer to execute such a method.
2. Description of the Related Art
As image forming apparatuses such as printers, facsimile machines, copiers, plotters, and multifunction machines having multiple functions of these apparatuses, those of a liquid ejection recording system using a recording head configured to eject ink droplets, such as inkjet recorders, are known. Image forming apparatuses of this liquid ejection recording system perform image forming (for which “recording” and “printing” may be synonymously used) on conveyed paper by ejecting ink droplets from a recording head onto the paper. These image forming apparatuses include serial image forming apparatuses and line image forming apparatuses. The serial image forming apparatus forms an image by ejecting liquid droplets while moving its recording head in a main scanning direction. The line image forming apparatus forms an image by ejecting liquid droplets without moving its recording head.
In the present invention, an “image forming apparatus” refers to an apparatus configured to form an image on media such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, and ceramics by causing ink to land on them. Further, “image forming (image formation)” refers not only to providing media with meaningful images such as characters and figures but also to providing media with meaningless images such as patterns (simply causing liquid droplets to land on media). Further, the term “ink” is used not only for what is called ink but also as a general term for all liquids with which it is possible to perform image forming, such as those called recording liquid, a fixing solution, liquid, and resin. Further, the term “paper,” which does not limit material to paper and includes overhead projector (OHP) sheets, cloth, etc., refers to what ink droplets are caused to adhere to, and is used as a general term for what are called a recording medium, recording paper, etc. Further, the term “image” not only refers to planar images but also includes images provided for three-dimensionally formed objects and images formed by shaping solid bodies three-dimensionally.
In serial image forming apparatuses, a linear encoder (position detector) that includes an encoder scale disposed along a main scanning direction of a carriage loaded with liquid ejecting heads and an encoder sensor configured to read the scale (position identifying part) of this encoder scale is provided to detect the position and the speed of the carriage, and the traveling speed of the carriage and the driving of the liquid ejecting heads are controlled based on the detection result.
Conventional linear encoders range from those magnetic to those optical. The magnetic linear encoder has the advantage that its performance is not affected by adhesion of a small amount of dirt on the surface of the linear scale. However, it is difficult to make the magnetic linear encoder higher and finer in resolution and to increase a gap between its linear scale and encoder sensor, and there are the problems of attachment accuracy and treatment of magnetized tools in the magnetic linear encoder. On the other hand, it is relatively easy to increase the gap between the encoder scale and the encoder sensor of the optical linear encoder, and the optical linear encoder is easy to assemble. Therefore, the optical linear encoder is suitable for increasing the resolution.
However, as linear encoders have become higher in resolution with increases in the speed and the accuracy of image forming apparatuses, the scattering of liquid such as ink inside the apparatus, a decrease in output due to adhesion of paper powder, and the influence of erroneous signals have become unignorable problems. For example, ink mist and/or paper powder adheres to an encoder scale and/or an encoder sensor during use over a long period to cause read errors, which causes problems such as a fuzzy recorded image due to carriage mispositioning and the stoppage of a machine due to occurrence of an error.
Therefore, image forming apparatuses are known that include a unit to clean the encoder scale. (See, for example, Patent Documents 1 through 3 listed below.)
On the other hand, in the serial image forming apparatus, vibrations are induced in the apparatus body by the reciprocating motion of a carriage loaded with recording heads. In particular, an increase in the carriage speed for increasing printing speed has caused the carriage to accelerate or decelerate suddenly at the time of performing scanning in a main scanning direction, which has increased the vibrations of the apparatus body. Further, in multifunction machines including an image reader (scanner), the above-described vibrations of the apparatus body caused on the side of an image forming part cause vibrations to the scanning by the scanner, thereby causing degradation of a read image.
Therefore, attempts have been made to prevent carriage vibrations. For example, it is known to reduce the vibrations of a carriage by attaching a vibration damping member having substantially the same mass as the carriage to a timing belt for moving the carriage and moving the carriage and the vibration damping member in opposite directions. (See, for example, Patent Documents 4 and 5 listed below.) In this case, it is also known to provide two carriages loaded with respective recording heads and control the movement of each carriage based on the result of reading a common encoder sheet. (See, for example, Patent Document 6 listed below.)    [Patent Document 1] Japanese Laid-Open Patent Application No. 2001-121721    [Patent Document 2] Japanese Laid-Open Patent Application No. 2005-169715    [Patent Document 3] Japanese Laid-Open Patent Application No. 2005-297514    [Patent Document 4] Japanese Laid-Open Patent Application No. 2001-138499    [Patent Document 5] Japanese Laid-Open Patent Application No. 2007-152899    [Patent Document 6] Japanese Laid-Open Patent Application No. 2003-341168